T-cell growth factor (TCGF) is a mitogenic protein released from mononuclear cells upon lectin or antigen stimulation. Detailed studies have shown that TCGF, which allows for the continuous proliferative culture of T cells, acts as the mitogenic stimulus after lectin/antigen activation. The aims of the current project are to purify TCGF, develop a radiolabeled TCGF-cell binding assay and produce monoclonal antibodies to TCGF and to the TCGF receptor. Other experimentation will be directed toward exploring the in vivo significance of TCGF and defining the mechanisms of TCGF production and action. It is hoped that these studies will provide new information and technical approaches which will lead to an increased understanding of the regulation of T cells in both physiological and pathophysiological states.